Influence of inflow conditions on turbine loading and wake structures predicted by large eddy simulations using exact geometry

A large eddy simulation was performed on an National Renewable Energy Laboratory (NREL) phase VI wind turbine (10m diameter), using the exact blade geometry, to determine the influence of different inflow conditions on the aerodynamic loadings and the near wake characteristics. The effects of the three inflow conditions, uniform inflow, linear wind shear and linear wind shear with turbulence, are investigated. Wind shear causes periodic variations in power and aerodynamic loading with an additional force component exerted along the lateral direction. Significant separation occurs in the high wind region on the suction side of the blades, resulting in unstable loading in off-design inflow conditions. Because of the shear effect between the near-blade tip vortex and ambient flow, the strong vortex core in the helical structure dissipates and transforms into a continuous vorticity sheet when x/D > 1.5. The combination of inflow turbulence and wind shear enhances the turbulence generation mechanism in the near wake, where energy is withdrawn from large wake structures and converted into energy of small-scale structures. Copyright (c) 2015 John Wiley & Sons, Ltd.